The embodiments disclosed hereinafter generally relate to systems and methods for reducing the trailing vortices and lowering the noise produced by the side edges of aircraft flight control surfaces or the tips of wings or rotor blades.
Over the years strict noise regulations have led to air traffic inefficiencies and reduced airport productivity. At many airports current capacity is largely controlled by the hours of operations, which are usually confined mostly to daylight hours to limit noise pollution at night. Consequently, noise reduction in airport environments has become an area of high priority in the aerospace transport industry. During takeoff, approach and landing noise is generated by the engines and airframe components. With the advent of high-bypass-ratio engines, significant reduction in engine noise has been achieved in recent years. Consequently, other noise sources have become more critical, with greater focus now being placed on airframe noise reduction. A major component of airframe noise is the high-lift system. In particular, flap elements produce high noise levels because of the tip vortex pattern.
Researchers in Europe as well as NASA have demonstrated substantial reduction in flap noise by using blowing jets at the side edges. The jets alter the vortex pattern, resulting in lower noise. The problem is that this method requires a significant amount of blowing to achieve meaningful noise reduction levels.
Blowing jets can be used to reduce flap noise by using a fluidic source, such as bleed air off an engine or a special-purpose compressor. The engine can be used to supply air for actuation. The requirement of engine bleed impacts the size of the engines. The larger the bleed amount, the heavier the engine, leading to an increase in airplane gross weight. In addition, engine efficiency is degraded due to bleed. Alternatively, a compressor can also be used in conjunction with a duct delivery system, but this also leads to significant additional weight.
Another problem is the vortex wakes of large transports. An area of high priority in the air transport industry is solving the looming problem of airport congestion. The capacity of many airports is close to saturation, yet the number of aircraft in commercial aviation is projected to increase. A factor in regulating landing and takeoff frequency is the time necessary for the dissipation of wake vortices produced by airplanes in motion. There is a pressing need for systems and methods for alleviating vortex wakes produced by airplanes during approaching and landing.
With respect to airplane wake alleviation, one solution is to avoid the flight path of large airplanes. Federal regulations require aircraft separation to be maintained to assure that severe vortex encounters are avoided. The minimum separation distance represents a key limiting factor of productivity at a growing number of airports around the world, with ripple effects on the entire air traffic system, not to mention passenger inconvenience. Airport congestion and delays translate to higher costs for air transportation. The incentive is very strong for finding a solution without compromising flight safety.
Wake alleviation is also a pressing need in the rotorcraft industry. For helicopters, the blade tip vortex passes close to the following blade, which, in certain situations, can lead to strong undesirable blade vortex interactions. The blade vortex interaction is the cause of noise from helicopters. Successful control of blade tip vortices can mitigate noise, enhance maneuverability and reduce operational hazard of helicopters.